Whenever I read why we have telomers, the answer is always so that we can replicate the end of the lagging strand. This is because the extreme end have a RNA primer to make the last Okazaki fragment, and after the removal of this primer it needs to somehow be replaced with DNA.I have the latest version of Molecular Biology of the Gene book (by Watson) in front of me and that's the only explanation provided.However, what about the beginning of the leading strand? I get that the end of the leading strand is easy to replicate, but the very beginning of the leading strand have one RNA primer, and how does this gets replaced with DNA? The only way I see possible is by having telomers, but yet I can never find this in books.

Replication of the leading strand begins at the origins and from those a continuous strand is produced until meeting replicating fork from another direction or end of the strand. The primer is removed by Okazaki fragment going in the other direction.